The present invention relates to fluid couplings for use, for example, in cooling fans for automotive internal combustion engines.
A fluid coupling for use in cooling fans for automotive internal combustion engines is disclosed, for example, in JP-U 57-204491 and JP-U 3-77825. The fluid coupling includes a housing relatively rotatably supported to a drive shaft driven by an engine crankshaft, an operation or partition plate for defining a storage chamber and a working chamber in the housing and having a communicating hole for fluid communication between the two, a rotor disposed in the working chamber and fixed to the drive shaft, a labyrinth torque-transfer part disposed at the outer periphery of the rotor and for transmitting torque of the rotor to the housing, and a valve mechanism for opening and closing the communicating hole of the operation plate in accordance with an ambient temperature of the housing to adjust a flow rate of working fluid flowing from the storage chamber to the working chamber.
The housing includes a main body supported to the drive shaft and a cover engaged with a front face of the main body. The cover has at the inner periphery thereof a circular recess for defining the storage chamber, and at the outer periphery of the recess a ring-shaped flange with a working-fluid return passage.
The operation plate is substantially circularly formed out of a metal plate, the outer periphery of which is joined to the inner periphery of the flange of the cover in a caulked way with an opening of the recess of the cover closed, which provides caulked-joint portions.
The torque-transfer part includes a plurality of concentric annular protrusions arranged at the outer periphery of the caulked-joint portions of the flange of the cover, and a plurality of concentric annular protrusions arranged with the rotor and engaged with grooves between the adjacent protrusions of the caulked-joint portions of the flange.
The fluid coupling is constructed as follows. When an ambient temperature of the housing is low, the communicating hole of the operation plate is closed through the valve mechanism to interrupt inflow of working fluid from the storage chamber to the working chamber. With this, supply of working fluid to the torque-transfer part is restricted to lower the amount of torque transmitted from the rotor to the housing, obtaining stop or low-speed rotation of a cooling fan. On the other hand, when an ambient temperature of the housing is high, the communicating hole of the operation plate is opened through the valve mechanism to produce large inflow of working fluid from the storage chamber to the working chamber and the torque-transfer part. With this, the amount of torque transmitted from the rotor to the housing is increased to produce high-speed rotation of the cooling fan, obtaining full cooling of an engine radiator.
With the fluid coupling, however, since the torque-transfer part is formed by engaging the protrusions of the cover of the housing with the protrusions of the rotor, its position of formation is restricted to the outer periphery of the cover. Noted that it is difficult to form the protrusions of the cover of the housing inside the outer peripheral edge of the operation plate, since the operation plate is mounted at the inner periphery of the cover.
Moreover, since the torque-transfer part is formed outside the inner peripheral surface of the storage chamber, i.e. the storage chamber is located upstream of the torque-transfer part, the torque-transfer part is immersed in working fluid accumulated in the storage chamber even during engine or rotor stop. This produces so-called accompanying rotation of the cooling fan upon start of engine operation.
Another fluid coupling which can prevent accompanying rotation of the cooling fan is disclosed, for example, in JP-U 59-128933 and JP-U 1-83925. This fluid coupling has a working-fluid accumulation chamber arranged at the outer periphery of the torque-transfer part. During engine stop, working fluid is accumulated in the working-fluid accumulation chamber to discharge working fluid from the torque-transfer part, thus preventing accompanying rotation of the cooling fan.
With another fluid coupling, however, since working fluid flows into the working-fluid accumulation chamber during engine operation, a residence time of working fluid is shorter in the torque-transfer part, resulting in a technical disadvantage of lowered utilization efficiency of working fluid.
A further fluid coupling is proposed which can overcome the above technical disadvantage. This fluid coupling includes in the working chamber a driven wheel arranged opposite to the rotor so as to define the torque-transfer part between the driven wheel and the rotor. A working-fluid passage is arranged with the driven wheel to bring working fluid out of the communicating hole of the operation plate to the torque-transfer part. This structure allows the torque-transfer part to be arranged inside the outer periphery of the operation plate, and not at the outer periphery thereof.
However, this fluid coupling produces difficulty of efficient and stable supply of working fluid to the torque-transfer part due to the magnitude of a flow resistance of the working-fluid passage of the driven wheel.
It is, therefore, an object of the present invention to provide a fluid coupling which contributes to efficient and stable supply of working fluid to the torque-transfer part and to accurate positioning and easy assemblage of the apparatus.
One aspect of the present invention lies in providing a fluid coupling, comprising:
a drive shaft;
a housing relatively rotatably supported to said drive shaft;
an operation plate arranged in said housing, said operation plate defining first and second chambers, said operation plate having a communicating hole for fluid communication between said first and second chambers;
a driven wheel arranged adjacent to said operation plate;
a rotor arranged in said second chamber, said rotor being fixed to said drive shaft;
a torque-transfer part interposed between outer peripheries of said driven wheel and said rotor, said torque-transfer part transmitting torque of said rotor to said housing;
a valve mechanism which opens and closes said communicating hole of said operation plate in accordance with an ambient temperature of said housing, said valve mechanism adjusting a flow rate of working fluid flowing from said first chamber to said second chamber;
a passage formed through said driven wheel, said passage bringing working fluid out of said communicating hole to said torque-transfer part;
an auxiliary chamber arranged between said driven wheel and said operation plate, said auxiliary chamber bringing working fluid out of said communicating hole to said passage; and
a positioning mechanism arranged between said operation plate and said driven wheel, said positioning mechanism ensuring circumferential positioning of said operation plate and said driven wheel.
Another aspect of the present invention lies in providing a fluid coupling, comprising:
a drive shaft;
a housing relatively rotatably supported to said drive shaft;
an operation plate arranged in said housing, said operation plate defining first and second chambers, said operation plate having a communicating hole for fluid communication between said first and second chambers;
a driven wheel arranged adjacent to said operation plate;
a rotor arranged in said second chamber, said rotor being fixed to said drive shaft;
a torque-transfer part interposed between outer peripheries of said driven wheel and said rotor, said torque-transfer part transmitting torque of said rotor to said housing;
a valve mechanism which opens and closes said communicating hole of said operation plate in accordance with an ambient temperature of said housing, said valve mechanism adjusting a flow rate of working fluid flowing from said first chamber to said second chamber;
a passage formed through said driven wheel, said passage bringing working fluid out of said communicating hole to said torque-transfer part;
means, arranged between said driven wheel and said operation plate, for bringing working fluid out of said communicating hole to said passage; and
means, arranged between said operation plate and said driven wheel, for ensuring circumferential positioning of said operation plate and said driven wheel.